Rotary dryers



Aug. 16, 1955 HALLDORSSON ROTARY DRYERS 4 Sheets-Sheet 1 Filed March 20,1953 INVENTOR if GisLzL ffaildorslson A TTOEA/E KS Aug. 16, 1955 G.HALLDORSSON ROTARY DRYERS 4 Sheets-Sheet 2 INVENTOR 07 ATTORNEYJ n! I IFiled March 20, 1955 V W "H". on hm V H v H h i q v M W w m w A i i u mw W flflnfln m. as R UON m 8% M 8m 8m 8m, 6% 8w ed A: J m w m O- Aug.16, 1955 HALLDORSSON ROTARY DRYERS 4 Sheets-Sheet 5 Filed March 20, 1953awn INVENTOR fizm ATTORNEXZS' 6, 1955 G. HALLDORSSON 2,715,283

ROTARY DRYERS Filed March 20, 1953 4 Sheets-Sheet 4 1N VENTOR GiyliHalldonssorv 0am, W

ATTORNEY United States Patent Ofiice 2,715,283 Patented Aug. 16, 1955ROTARY DRYERS Gisli Halldorsson, Baltimore, Md., assignor to Edw.Renneburg & Sons Co., Baltimore, Md., a corporation of DelawareApplication March 20, 1953, Serial No. 343,539

5 Claims. (Cl. 34-79) This invention pertains to improvements in rotarydryers for fish meal and analogous material in which the material ispassed through the rotating dryer in contact with a stream of heated airin such manner that it is commercially dried at the outlet end of thedryer.

Dryers of this type generally comprise continuous elongate cylinders ofconstant diameter through which is forced a draft of heated air, thematerial to be dried be ing introduced at the inlet end of the rotatingcylinder and carried therethrough in contact with the heated air draft.In constant diameter cylinders of this type the speed of the drying airis constant throughout the length of the cylinder except for variationof gas volume due to temperature and humidity changes. The temperatureof the air stream gradually decreases from inlet to exhaust end, whereasthe relative humidity increases. The velocity usually remains high andit is necessary to provide a drying cylinder of extreme length in orderto assure a satisfactory drying time for the material during itscomparatively rapid passage through the drying cylinder. The cost andspace requirements of such elongate cylinders are high and the productresulting is frequently improperly dried and unsatisfactory. Further,scorching or burning of the material frequently occurs at the inlet end.

It is therefore a primary object of the present invention to provide animproved rotary dryer of varied diameters wherein the speed of the airstream and particles is controlled in the various sections of the dryerto provide a high velocity for the particles at the feed or inlet end ofthe dryer, a considerably lower velocity for the particles passingthrough the central portion thereof and a very much lower velocitytoward the discharge end of the dryer, to assure a completely dried andunscorched product at the discharge end of the dryer, Where the temperature is lowest and the material may remain for a prolonged periodwithout being damaged from heat.

It is a further object of this invention to provide an improved dryer inwhich danger of burning or scorching of the particles at the hot feedend thereof is eliminated and a complete drying of the larger particlesis accomplished.

It is a further object of this invention to evolve a rotary dryer ofimproved internal configuration and shorter length than conventionaldryers of similar capacity.

It is another object of this invention to provide improved means forrecirculating the drying air to the inlet end of the dryer, usuallyafter washing and removal of moisture by condensation, for reuse in thedrying operation.

It is a further object of this invention to provide means fordeodorizing the recycled gases by passing a portion of the recycledgases through the hottest part of the furnace where they are incineratedand then discharging these incinerated gases through a stack to theatmosphere.

It is a further object of this invention to provide an improved,enlarged chamber at the discharge end of the dryer, wherein largerparticles of material will be re- Cit tained and dried internally beforefinal delivery to the collector.

It is another object of this invention to provide improved and easilyremovable conveyor flights with changeable pitch within the rotarydryer.

Other and further objects of this invention will become apparent as thisspecification proceeds.

Referring to the drawings, Fig. 1 is a perspective View, partially insection, taken from one side of the rotary dryer, showing the improvedfurnace and dryer structure and the drying air recirculating system;

Fig. 2 is a cross sectional view taken at the discharge end of the dryeron line 3-3 of Fig. 1;

Fig. 3 is a cross sectional view of the improved dryer, taken on itslongitudinal axis, illustrating schematically the arrangement of theflights about the interior periphery of each section thereof;

Fig. 4 is cross-sectional view of the flights, showing the preferredshape of each;

Fig. 5 is a plan view of a special type of complete installationutilizing the improved rotary dryer;

Fig. 6 is a partial end view taken from the furnace end of the dryer andFig. 7 is a partial end view taken "tom the discharge end of the dryerand showing the an, duct, collector and condenser and Wash towerstructure.

In the drawings, Fig. l, 6 indicates the furnace or air heating chamber,7 indicates the narrow entry neck of he rotary dryer, 8 indicates theoutwardly expanded ection of the dryer, 9 indicates the elongate,constant diameter section thereof, 10 indicates the enlarged retentionand terminal drying section of the dryer, 11 indicates the narrowed exitneck of the dryer, 12 indicates the vortical flow meal collector and 13indicates the air recirculating or recycling duct extending from theupper extremity of the flow meal collector to the condensing and washtower W and thence to the recycling fans located at the face of thefurnace structure. As there are novel aspects to each of the elements ofthe entire dryer structure each element will be considered in detail,from the furnace through the recycling and condensing and wash towerstructure.

Referring to furnace 6, it is preferably of substantially rectangularcross-section and is appropriately lined with fire-brick or otherheat-resistant material. Furnace 6 is provided at its outer face with aport 14 in which are disposed the burners or nozzles 15 of appropriateoil burner equipment 16 which is preferably disposed outwardly of thelower face of the furnace. Let into the outer furnace wall, above port14, is an appropriate air duct or vent 17 through which recycled airfrom conduit 13 is delivered into the peripheral portion of furnace 6outwardly of internal baffles 18 by recycling fan or fans 19 which aredisposed adjacent the outer, upper wall of furnace 6 outwardly of vent17 and at the extremity of recycle conduit 13. As shown, internal baffle18 generally conforms to the internal configuration of furnace 6 in suchfashion as to provide an outer passage 20 for recycled air, leading tothe neck 21 thereof. A portion of the recycled air and gases, will beled into duct 14, adjacent burners 15, and thence into the maincombustion chamber of the furnace where these gases are incinerated atthe hottest point in the furnace. An outlet vent v is provided in thefurnace Wall adjacent this incinerating area for discharging theseincinerated and deodorized gases into a stack S, through which theincinerated and deodorized gases pass to the atmosphere. Stack S, asshown, is provided adjacent its upper extremity with a damper d, whichmay be adjusted to open or close stack S to the atmosphere.

Fire bridge 22 is provided extending upwardly at an obtuse angle at theinterior end of furnace 6 to provide a shield for the material to betreated and to prevent burning or scorching thereof in neck 21.

passage 26 and assists in blowing the disintegrated ma terial throughpassage 25 into neck 21. A conventional over-feed arrangement extendinginto the dryer throat may be used. 7

Extremely high temperatures, i. e. on the order of 3000 toy35 F., aregenerated in a limited space in front of the burner in the combustionchamber of furnace 6 Where incineration of part of the recycled gasestakes place and whence incinerated and deodorized gases pass up thestack S. It is an important object of this invention to eliminatescorching or burning of the material in the neck 21 of furnace 6 and inconstricted neck portion 7 of the dryer, Where operating temperaturesare much lower. 7

The functioning of the furnace structure will be discussed at morelength later in this specification.

Furnace 6 provides the necessary heat for heating the drying air beforeits passage through the rotary dryer. It also acts to incinerate aportion of the recycled gases, as will be discussed further. The dryingair is pulled through the rotary dryer by means of a centrifugal fan 27rotatably mounted at the discharge end of the dryer adjacent therestricted exit neck 11 thereof in the base of vertical duct 28'whichdirects the heated air stream and entrained material to the upperextremity of vertical flow meal collector 12, as will be discussed inmore detail. 7

Referring to the rotary dryer structure perse, it will be noted thattherotary dryer comprises broadly a narrow entering neck 7, which ispreferably of cylindrical shape and of relatively small diameter, anoutwardly enlarging conical section 8, an elongate medial portion9 ofconstant diameter, extending into an enlarged retention.

cylindrical drying chamber 10 of comparatively short length, a shortconical section and a small diameter cylindricalexit neck 11. In'cases'where it is not desirable to remove the material by air, theretention chamber 10 may serve as the extreme outlet end of the dryer,

opening into a backbox and discharging the material diwhich registerswith a chain drive 36 provided about the outer periphery of retentionsection 10 of the dryer. The drive may be of the gear type or of thefriction type, if desired, using heat resistant rubber as the drivingsurface for the rollers, where low surface temperatures of the runningbands may make this feasible.

An appropriate conical seal 38 is provided about the entry end of neck-7of the dryer and is aflixed about the outer periphery of neck 21 offurnace 6. Entry neck 7 is of restricted diameter to provide highinitial velocity to the highly heated air and entrained material at theentry end of the rotary dryer. From entry neck 7 theshell of the dryeris gradually widened in conical section 3 to gradually increase thediameter of the dryer and to decrease the speed of the hot air andmaterial, prior to its entry into elongate cylindrical section 9 of thedryer.-

Enlarged retention chamber 10 is provided at the terminal extremity ofthe dryer. As a result of its enlarged diameter air entering retentionchamber 10 from section 9 drops considerably in velocity whereby section10 acts as a trap or holding station for large, internally moistparticles of the material. The particles trapped within section 10 aremaintained in this section of the dryer until they are sufficientlyinternally dried, at which time their weight is reduced to a point wherethey are light enough to be carried ofl by the air stream intoattenuated neck portion 11 at the terminal end of the dryer, wherein airvelocity rapidly increases. air draws the enlarged dry particlesupwardly into duct 28 for delivery into the upper section of verticalflow meal collector 12.

The interior of each of the sections of the rotary dryer 1 is preferablyprovided with flights 37 peripherally disposed about their interiors, asshown in Fig. 3. This arrangement of the flights, as shown in Fig. 3, isdesigned to provide a heavy showering of the material in the initial endof the dryer where the flights are higher than in the medial andterminal portions thereof. In

the latter portion of the dryer care must be taken to shower thematerial more thinly to prevent its being blown away too rapidly and toinsure its retention within the dryer for the required length of time toinsure satisfactory drying.

The flights 37, as shown, are preferably spaced equidistant from eachother about the inner peripheries of vided, to produce a heavy showeringof the material in i this section.

' A cross-sectional view of the various individual flights is shown inFig. 4 of the drawings. This view illustrates the respectiveangularities of each of flights A, B and C. It will thus be seen thatflight A comprises an elongate flight with its extremity inclined at anacute angle to.

its'rectilinear section, flight B comprises a short rectilinear flight,lacking the angular extremity of flight A, and flight C comprises aflight similar to flight A, but with its extremity inclined at a rightangle to its rectilinear portion.

Referring to Fig. 3, section 2a of the dryer is preferably provided withflights A, B and C of less height-than the spiral flights in section 1a,i. e. where, for example, the

height of the spiral flights in section 1a is 8", the. height of therectilinear portions of flights A, B and C in section 2a will be 6". ispreferably AB'ACA-B-A-C.

In section 3a of the dryer, the height of the flights is preferably onehalf the height of the flights in section 2a, i. e. 3", and the order ofthe flights is: BCB- AB--C.

In section 4a flights of the same height as in section 3a are utilized,the order being preferably ABA CA.

Section 5a carries flights of the same height as section 4a, preferablyarranged BCBA-B.

Section 6a carries flights of the same height as section 5a, preferablyarranged ABAC-A.

Sections 7a12a, inclusive, also carry flights of thesame height as insection 6a, preferably arranged B-A BCBA.

Each flight section is preferably offset 3" with respect. tothe'preceding section, as shown, and the flight profiles are matched toinsure even showering of the material.

The arrangement of the flights as shown in Fig, 4

sure that the material not be blown away too quickly, but be retainedwithin these latter sections for a time sufficient to insure properdrying therein.

Each flight is preferably bolted in each section by two bolts,directly'to the dryer shell, to' permit easy This high velocity Theorder of the flights in section 2a removal and change of the flightsdepending upon conditions. Each flight may be supplied with a third orextra bolt hole, as shown, to permit arrangement in spiral, Wheredesired.

The normal position of the flights in sections 2a-12a, inclusive, asshown, is parallel to the longitudinal axis of the dryer. Thisarrangement may be varied as required by local conditions and dependingupon the speed with which it is desired to pass the material. Toincrease retention time, some or all of the flights in any of thesections may be removed. I

The heights of the flights given is by way of illustration only and maybe varied as required, depending upon conditions. The respective heightsof the flights should, however, be maintained.

As shown in Figs. 1 and 6, the base of duct 28 is appropriately enlargedto contain centrifugal fan 27. Fan 27 is preferably of the materialhandling industrial type and is aligned with cylindrical extension 40 atthe lower extremity of duct 28. The outer periphery of extension 40extends into conical section 41 affixed about the outer periphery ofterminal section 11 of the dryer. Fan 27 is preferably sealed andmaintains the furnace under a negative pressure whereby air will bepulled into the furnace through all openings connecting it with theatmosphere at furnace level. This fan must overcome the resistance inthe furnace and dryer on the suction side to provide the air and gaseswith suflicient velocity to discharge them through the dryer. Fan 27 ispreferably driven from a motor 42 through a suitable belt drive 43. Fora dryer of the size here described, this motor is preferably ofapproximately 75 horsepower and the fan should handle up toapproximately 75,000 C. F. M. of air at 200 F. and must be able tooperate under from 300 to 400 F. temperature.

Referring back to the rotary dryer, as has been previously stated theflights in each cross section of the dryer should be arranged to showerthe material in each cross section as evenly as possible. There areseveral types of flight profile in each section of the dryer. Theflights should be so arranged in each section as to keep the materialevenly distributed, over each section, leaving no passage through whichthe drying air may short circuit. The flights are generally arranged toserve this purpose of equal distribution of the material in eachsection. They are arranged so that the material will not shower until itnears the upper section of the dryer. The flights in some sections maybe inclined axially to throw the material rearwardly, depending upon thespeed at which it is desired to pass the materiad through that section.

The normal speed of rotation of the dryer is from 3-8 R. P. M., whichspeed may be varied depending upon the nature of the material beingtreated and the specific drying problem involved.

The drive for the dryer may be by means of a band gear driven by apinion on the motor reducer 34, or it may be by sprocket gear and chaindrive from the motor reducer or by a friction drive using heat resistantrubber or neoprene rubber as surfaces for the driving rollers.

As has been stated previously, the air velocity in the dryer is at itslowest in the enlarged retention chamber thereof in which large,partially moist particles are trapped and circulated for a considerableperiod of time until they are properly dried internally, at which timetheir weight is sufliciently reduced to allow them to be pulled out ofsection 10 by the comparatively high velocity air in restricted necksection 11 of the dryer. From neck section 11 they pass up through duct28 into the top section of vortical collector 12. The properly driedmaterial falls by gravity into the lower section of collector 12 and isappropriately sacked or blown to the storage room therefrom.

The temperatures in the dryer decrease rather rapidly from their highestpoint at throat 21 of the furnace where the air enters narrow neck 7 ofthe dryer at temperatures on the order of 600 F. The flash evaporationof free surface moisture drops the temperatures to approximately 400 F.in conical section 8 of the dryer and the air temperature is furtherreduced in cylindrical section 9 thereof to approximately 250 to 300 F.at the inlet to enlarged retention section 10 thereof. In retentionsection 10, the air temperature drops further to 200 to F thetemperature of the material therein being somewhat lower.

The air velocities in the dryer vary. The conveying velocity in dryerthroat 7 is approximately 2400 F. P. M., which drops to 1500 F. P. M. inconical section 8 and to about 1300 F. P. M. in elongate cylindricalsection 9. It is about 1200 F. P. M. at the end of section 9, where itenters Roto Cyclone section 10. The air velocity in section 10, whichhas almost twice the cross-sectional area of cylindrical section 9,drops to less than half of the velocity in sections 8 and 9 to about 500to 700 F. P. M., resulting in retention in enlarged section 10 of large,partially dried particles of the material. These large particles remainin section 10 until sufficiently dry and light to be carried off throughneck 11 of the dryer, where velocities again rise to approximately 2400F. P. M.

Normally, the drying air is recycled, as shown in Fig. 1, recycle duct13 being provided communicating between the upper extremity of vorticalflow meal collector 12, condensing and wash tower W and recycling fans19, at the face of the furnace.

Condensing and wash tower W has a dual function in recycling duct 13. Itis provided about its interior with water sprays through which therecycled air is passed and which dissolve water soluble gases andimpurities in the recycled air. Further, the sprays condense themoisture contained in the recycled air and this moisture runs down thewalls of the tower and is entrapped in a water trap at the base of thetower. Thus, the recycled gases are both dried and partially purified inthe condensing and wash tower and are conditioned for repassage throughthe furnace and dryer.

Duct 13 is provided at its lower, outer extremity with a damper or vent46 which may be opened, as desired, to regulate the amount ofatmospheric air pulled into the furnace chamber by recycling fans 19.This fresh air can also be admitted through feed 24 and passage 25.Recycling fans 19 may be of the axial-flow or of the centrifugal typeand are driven from a motor 47 provided for that purpose. Fans 19 drawthe heated air through duct 13 and condensing and wash tower W,assisting fan 27 in its action of exhausting or pulling the air throughthe furnace and dryer and discharging it through the collector.

Referring to Fig. 5 of the drawing, one special embodiment of a completeinstallation utilizing the improved dryer structure of the presentinvention is illustrated. In this installation for non-oily raw fish,Where no press is used, the raw fish is first elevated into the indirectcooking chamber by an elevator 50. After cooking in cooker 51 the cookedfish is delivered to a disintegrator 52 whence it is delivered to throat21 of furnace 6, whence it is delivered into the rotary dryer structure.The heated air and entrained material are pulled through the rotarydryer by means of the fan 27 and thence into the cyclone collector. Fromthe collector the dried material is delivered by meal conveyor 53 togrinder 54 where the bulk of it is bagged or blown into the storageroom. A recycling conveyor 55 is provided to recycle part of the mealback to the disentegrator 52 where it is used to condition the wetmaterial by making it more suitable for drying. This is merely oneillustration of a complete installation designed to utilize the improvedrotary dryer. In this particular type of installation meal recovery isincreased 20 to 25% over that in conventional installations usingpresses. Many other modified installations have been developed utilizingthe improved rotary dryer.

' also of the moisture content.

The feed mechanism for the dryer may be varied in many respectsdepending upon the nature of the material being dried and the probleminvolved.v A screw conveyor may be utilized, combined with adisintegrating mill to refine the particles before entering the dryerthroat. The material may be fed to the dryer by an underfeed or anoverfeed screw and introduced by paddles into the dryer throat, wheretheair stream of highly heated air will carry it into the dryer. As analternative, a combined disintegrator-blower may be utilized, or asteam-heated, hollow screw conveyor under pressure may be used to blowthe material into the dryer throat. The release in pressure in aninstallation of this type assists in exploding the material fromwithinand shortens the drying time.

The dimensions of the various sections of the rotary dryer may be variedwithin a wide range depending upon the nature of the product to bedried, the volume to be handled and upon various other factors. Thediameters of the various sections of the dryer are selected inaccordance with the air volumes which have to pass through L eachsection to carry heat and moisture and by the air velocity required inthe particular section. This air volume is a function of the air weightand temperature and The maximum desirable material speed through eachsection is also not constant but varies with moisture content andtemperature. Further, the axial movement of the material, whichgradually becomes lighter as it is dried, is a variable function of theair velocity and also of the rotation of the dryer. These constants canbe varied in the field to suit conditions.

The dimensions of the dryer illustrated in the draw ings are preferablyas follows: Neck 7, 7 diameter 42" length; conical section 8, 79 indiameter 48" length; cylindrical section 9, 9' diameter 28 length;conical section between sections 9 and 10, 9-12 diameter 18" length;enlarged retention section 10, 12 diameterXl7 length; tapered sectionbetween retention section 10 and restricted section 11, 12-7 diameter l8length; 'neck section 11, 71" diameter 54 length. These dimensions areby way of illustration only and may be varied as desired providing theproportionate sizes are maintained.

The furnace unit used with a dryer of these dimensions would be on theorder of 24 feet 18 feet l2 feet with a volume of about 1800 cubic feetand a maximum capacity of 60,000,000 B. t. u. per hour. A furnace ofthis capacity would handle press cake from 60 to 80 tons of raw fish perhour when using normal high temperature drying of from 1200 to 600 F.,depending upon the moisture in the press cake. For low temperaturedrying of from 600 to 200 F. only about half of this capacity would beutilized and the unit would handle twenty-five to thirty tons per hour.

Dryer. neck 7 is preferably 7 feet in diameter and 42 in length.Discharge neck 11 at the delivery end of the dryer is preferably 71" indiameter and 54" in length. These two extremities of the rotary dryerare the high velocity sections thereof, the high velocity being requiredin throat 7 to prevent scorching or burning of the meal therein. Thehigh velocity at terminal section 11 of the dryer is necessary in orderto pull particles of meal from enlarged section 10 of the dryer andforce the entrained particles upwardly through conduit 28 into thevortical flow collector 12.

The overall operation of the improved dryer is as follows: the fish mealor press cake in disintegrated condition is delivered ot the highvelocity, high temperature throat 21 of the furnace structure by meansof an appropriate screw feed and air blast 23 whence it is blown by thehigh velocity stream of heated air into the narrow neck section 7 of thedryer. Velocity of the air stream is high in neck section 7 to pull thematerial rapidly therethrough and prevent scorching or burning of themeal at this high temperature point in the dryer. Ternt3 peratures atthis point in the throat of the dryer attain 600 F. If the material weremaintained for an appreciable time in the throat 7 at these temperaturesit would tend to be scorched or burnt. From section 7 the partiallydried material is delivered into conical or enlarging section 8, whereair velocity decreases and further drying takes place. From section 8the material passes into cylindrical or quick drying section 9 where itis subjected to a reduced air velocity and temperature, drying of smallparticles being substantially completed and internal drying of thelarger particles being initiated. From elongated cylindrical section 9the particles are carried into enlarged retention section 10 of across-sectional area substantially twice as large as that of section 9.In enlarged section 10 the larger particles are trapped and aremaintained under rotation and agitation, subject to comparatively lowtemperature and velocity drying air, until they are completelyinternally dried and are light enough to be carried out of section 10by. the high velocity air passing through restricted terminal section 11at the discharge end of the rotary dryer. After passing throughrestricted section 11 the large and small particles are forced upwardlythrough duct 28 into the upper section of vortical flow collector 12where they are collected for bagging or for blowing into the storageroom. As shown in Fig. 1, the drying air may be recycled from the upperextremity of vortical collector 12 back to the recycling fans 19 bymeans of recycling duct 13, through condensing and wash tower W. Thisrecycling of the drying air is especially necessary where conditionsrequire scrubbing and incineration of gases passing to the atmosphere toeliminate objectionable odors and fumes. On each run the drying air willpick up moisture from the material and discharge it in the condensingand wash tower. A portion of the oxygen of the air will be consumed bycombustion and a corresponding amount of atmospheric air required forcombustion must be introduced for each drying cycle. A correspondingamount of incinerated gases thus must be discharged from the system foreach cycle. Therefore, a large quantity of air may act as drying mediumfor carrying water vapor at low temperatures, recycling again and again,and only a small portion thereof is discharged to the atmosphere.Recycling maintains the heat of the recycled air to a certain extent,even when the recycled air is washed, and thus is a considerable factorfor fuel saving. Recycle ducts 46 may be adjusted automatically bythermostats and humidistats to control the amount of atmospheric airintroduced into the system adjacent recycling fans 19.

A portion of the recirculated air which would normally be dispelled totheatrnosphere is introduced into the combustion compartment of thefurnace adjacent the burners whereby the gases immediately reach a veryhightempera= ture and are thus incinerated. The fresh air is introducedperipherally about the combustion chamber of the furnace or at thefurnace throat in such fashion that it passes through the normal dryingcycle before taking part in the combustion. The incinerated air isconveyed through a vent v to the stack S and dispersed to theatmosphere.

The essence of the present invention lies in the novel, varied diameterconstruction of the rotary dryer, in the novel, adjustable flightarrangements therein and in utilizing one furnace for heating the airand incinerating waste gases, instead of two, as is now customary. Byutilizing a rotary dryer constructed in conformity with this disclosureit is possible to obtain an improved drying of fish meal and othermaterials at lower temperatures and with less space requirements thanwas possible with previous equipment. By utilizing the novel dryerstructure disclosed loss due to scorching and burning of the mealparticles is eliminated and a highly improved product results. Further,due to the enlarged retention chamber and the other novel features ofthe dryer, one of these dryers will handle the capacities of severalconventional units, resulting in lower capital investment and operatingcosts.

The invention is subject to numerous modifications without departingfrom the spirit thereof. The dryer may be utilized in many differenttypes of installations to great advantage, the essence of this inventionlying in the improved configuration of the rotary dryer structureitself.

Attention is directed to the appended claims for a limitation of thescope of the invention.

What is claimed is:

1. In a rotary dryer, a furnace, a fan disposed at the face of saidfurnace for introducing air therethrough, a rotary dryer horizontallymounted adjacent the neck of said furnace and comprising a restrictedcylindrical section, an enlarged outwardly diverging conical sectionadjacent said restricted cylindrical section, an extended cylindricalsection adjacent said conical section, an enlarged cylindrical retentionsection adjacent said extended cylindrical section, a converging conicalsection at the terminal end of said enlarged cylindrical section, saidsections being arranged end to end along a common axis, fan meansadjacent said neck disposed in the lower extremity of a verticallyextending duct, a vertical collector disposed adjacent said duct andreceiving the upper extremity thereof and a recycle duct for heated aircommunicating between the upper extremity of said collector and saidrecycle fan means at said furnace.

2. A rotary dryer for fish meal and analogous material comprising afurnace, a rotary dryer rotatably mounted adjacent the mouth of saidfurnace and communicating therewith, comprising a restricted cylindricalneck section, an outwardly widened section communicating with said necksection, an elongated cylindrical section of constant diameter adjacentsaid outwardly widened section, a retention section of greatly enlargeddiameter and short length adjacent said elongated cylindrical sectionand reducing into a narrow cylindrical neck at the terminal end of thedryer, said sections being arranged end to end along a common axis, anupright duct adjacent the end of said dryer and communicating therewith,a fan rotatably mounted in the lower extremity of said duct adjacent theend of said dryer, a collector stack vertically disposed adjacent saidduct and communicating therewith at its upper extremity, a recycle ductextending from the top of said collector to the face of said furnace,fans rotatably mounted in the extremity of said recycle duct adjacentsaid furnace and communicating therewith to pull air through said ductand into said furnace, an air vent in said recycle duct, wherebymaterial delivered into the neck of said furnace will be blown throughsaid rotary cylinder in stages and delivered into said collector in acompletely dry condition.

3. A rotary dryer comprising a restricted cylindrical neck section, anoutwardly enlarged conical section adjacent said neck section, anelongated section of constant diameter adjacent said conical section, aretention section of greatly enlarged diameter and comparatively shortlength adjacent said elongated section and a terminal section of greatlyreduced diameter adjacent said retention section said sections beingarranged end to end along a common axis whereby the velocity of materialladen air drawn through said dryer will vary in an inverse ratio to thevarious diameters of the sections of the dryer.

4. In an improved rotary dryer, a furnace, fans disposed at the face ofsaid furnace for forcing air therethrough, a rotary dryer horizontallymounted adjacent the neck of said furnace and comprising a restrictedcylindrical section, an enlarged outwardly diverging conical sectionadjacent said restricted cylindrical section, an extended cylindricalsection adjacent said conical section, an enlarged cylindrical retentionsection adjacent said extended cylindrical section, a narrow restrictedneck at the terminal end of said enlarged cylindrical section, a seriesof staggered conveyor flights of gradually decreasing heightperipherally arranged in each of said sections, fan means adjacent saidneck disposed in the lower extremity of a vertically extending duct, avertical collector disposed adjacent said duct and receiving the upperextremity thereof and a recycle duct for heated air communicatingbetween the upper extremity of said collector and said recycle fan meansat said furnace.

5. In an improved rotary dryer, a furnace, fans disposed at the face ofsaid furnace for forcing air therethrough, a rotary dryer horizontallymounted adjacent the neck of said furnace and comprising a restrictedcylindrical section, an enlarged outwardly diverging conical sectionadjacent said restricted cylindrical section, an extended cylindricalsection adjacent said conical section, an enlarged cylindrical retentionsection adjacent said extended cylindrical section, a narrow restrictedneck at the terminal end of said enlarged cylindrical section, a seriesof graduated and staggered flights of decreasing height afiixed withineach of said sections, fan means adjacent said neck disposed in thelower extremity of a vertically extending duct, a vertical collectordisposed adjacent said duct and receiving the upper extremity thereofand a recycle duct for heated air communicating between the upperextremity of said collector and said recycle fan means at said furnace.

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